US8184986B2 - Detection arrangement - Google Patents

Detection arrangement Download PDF

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US8184986B2
US8184986B2 US11/793,104 US79310405A US8184986B2 US 8184986 B2 US8184986 B2 US 8184986B2 US 79310405 A US79310405 A US 79310405A US 8184986 B2 US8184986 B2 US 8184986B2
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path
filter
information
pair
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Remi Oseri Cornwall
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/70—Photonic quantum communication

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  • This invention relates to a detection arrangement and an information transmission arrangement, and in particular to an information transmission arrangement for allowing efficient communication of information.
  • one aspect of the present invention provides a detection arrangement comprising: a splitter; a detector, first and second paths being defined between the splitter and the detector and the splitter being arranged to direct an incoming particle along the first or second path depending upon the value of a parameter of the incoming particle; and a manipulation arrangement located on at least one of the first and second paths, so that, if a particle in a superposition of values of the parameter impinges on the splitter and a wavefunction of the particle is directed along both the first and second paths, the manipulation arrangement will act on the wavefunction to allow interference, at or near the detector, between the portions of the wavefunction that were directed along the first and second paths.
  • the splitter is a polarising splitter and the parameter of the incoming particle is the direction of polarisation of the incoming particle.
  • the polarising splitter is arranged to direct particles having a first direction of polarisation along the first arm, and particles having a second direction of polarisation along the second arm, wherein the first and second directions of polarisation are different from one another by approximately 90°.
  • the manipulation arrangement comprises a rotator arrangement provided on the first path and operable to alter the direction of polarisation of polarised particles passing along the first path.
  • the rotator arrangement is operable to alter the direction of polarisation of polarised particles passing along the first path by approximately 90°.
  • first and second rotator arrangements are provided on the first and second paths respectively and are operable to alter the direction of polarisation of polarised particles passing along the paths.
  • the rotator arrangements are operable to alter the directions of polarisation of the particles so that the difference between the directions of polarisation of particles passing along the paths is altered by 90°.
  • the manipulation arrangement comprises a manipulation particle source that is arranged to emit particles in such a way that they may interfere with a portion of a particle wavefunction passing along the first path, to give a resultant wavefunction that has at least a component having a direction of polarisation approximately equal to that of a portion of a particle wavefunction directed along the second path by the polarising splitter.
  • the manipulation arrangement further comprises a further polarising splitter located on the first path and arranged to direct an incoming particle towards the detector or in an alternative direction depending upon the direction of polarisation of the incoming particle.
  • the manipulation particle source is arranged to emit particles towards the further polarising splitter, so that particles emitted thereby may interfere with at least a portion of a particle wavefunction that is directed towards the detector by the further polarising splitter.
  • the manipulation arrangement further comprises a phase alteration component that is arranged to alter the effective path length of the first path.
  • the effective lengths of the first and second paths are such that, if a particle in a superposition of values of the parameter impinges on the polarising splitter, a wavefunction of the particle is directed along both the first and second paths and interference occurs between the portions of the wavefunction that were directed along the first and second paths, the interference will be destructive at the detector so no particle will be detected by the detector.
  • the particle will be directed to the detector for detection thereby.
  • Another aspect of the present invention provides an information transmission arrangement comprising: an information particle source; a filter provided at a first location, the filter being configured only to allow particles having a certain value of the parameter to pass therethrough; and a detection arrangement provided at a second location, the detection arrangement being operable to distinguish between an incident particle having a determined value of the parameter and an incident particle in a superposition of values of the particle.
  • the detection arrangement is a detection arrangement according to any of the above.
  • the parameter is the direction of polarisation of a particle
  • the filter is a polarising filter
  • the information particle source is operable to emit particle pairs, one particle in each pair being directed towards the filter and the other particle in each pair being directed towards the detection arrangement.
  • the filter may be moved between an on-path position, in which the one particle in each particle pair passes though the filter, and an off-path position, in which the one particle in each particle pair does not pass though the filter.
  • the particles emitted by the information particle source are matter particles.
  • a further aspect of the present invention provides an information transmission arrangement comprising: an information particle source, operable to emit pairs of particles, a first particle in a pair being emitted towards a first location and a second particle in a pair being emitted towards a second location; a filter provided at the first location, the filter being moveable between an on-path position, in which the one particle in each particle pair is absorbed by the filter, and an off-path position, in which the one particle in each particle pair is not absorbed by the filter; and a detection arrangement provided at the second location, the detection arrangement being operable to distinguish between an incident particle having a relatively short coherence length and an incident particle having a relatively long coherence length.
  • the information particle source comprises a sample of a material having at least a three-level atomic structure, one of the particles of a particle pair being emitted as an electron moves from a first level to a second level within the structure and the other one of the particles of the particle pair being emitted as the electron moves from the second level to a third level within the structure.
  • the detection arrangement comprises: a splitter; and a detector, first and second paths being defined between the splitter and the detector, a path length of the first path being longer than a path length of the second path, the arrangement being such that, if a particle impinges on the splitter and a wavefunction of the particle is directed along both the first and second paths, the portions of the wavefunction that were directed along the first and second paths may interfere with one another at or near the detector.
  • the information particle source is operable to emit pairs of particles whose wavefunctions are entangled with one another.
  • the path length from the information particle source to the filter is less than the path length from the information particle source to the detection arrangement.
  • a pair of path length modules are provided, each of the path length modules having an input and an output and defining a path length therebetween, the path lengths of the path length modules being substantially identical to one another and hidden from an observer of the path length modules, one of the path length modules being placed so that particles travelling from the information particle source to the filter pass therethrough and the other of the path length modules being placed so that particles travelling from the information particle source to the detection arrangement pass therethrough.
  • the particles emitted by the information particle source are photons.
  • Another aspect of the present invention provides an information transmission arrangement comprising first and second transmission arrangements to the above arranged so that the filter of the first transmission arrangement is located near the detection arrangement of the second transmission arrangement and the filter of the second transmission arrangement is located near the detection arrangement of the first transmission arrangement.
  • a further aspect of the present invention provides a method for detecting particles comprising the steps of: providing a detection arrangement according to the above; and directing an incoming particle into the detection arrangement.
  • Another aspect of the present invention provides a method for transmitting information comprising the steps of: providing a filter configured only to allow particles having a certain value of a parameter to pass therethrough; providing a detection arrangement operable to distinguish between an incident particle having a determined value of the parameter and an incident particle in a superposition of values of the particle; providing an information particle source operable to emit particle pairs, one particle in each pair being directed towards the filter and the other particle in each pair being directed towards the detection arrangement; and moving the filter between an on-path position, in which the one particle in each particle pair passes though the filter, and an off-path position, in which the one particle in each particle pair does not pass though the filter.
  • the detection arrangement is a detection arrangement according to the above.
  • a further aspect of the present invention provides a method for transmitting information comprising the steps of: providing a filter configured only to absorb particles that are incident thereon; providing a detection operable to distinguish between an incident particle having a relatively short coherence length and an incident particle having a relatively long coherence length; providing an information particle source operable to emit particle pairs, one particle in each pair being directed towards the filter and the other particle in each pair being directed towards the detection arrangement; and moving the filter between an on-path position, in which the one particle in each particle pair passes though the filter, and an off-path position, in which the one particle in each particle pair does not pass though the filter.
  • the step of providing an information particle source comprises providing a sample of a material having at least a three-level atomic structure, one of the particles of a particle pair being emitted as an electron moves from a first level to a second level within the structure and the other one of the particles of the particle pair being emitted as the electron moves from the second level to a third level within the structure.
  • the step of providing a detection arrangement comprises providing: a splitter; and a detector, first and second paths being defined between the splitter and the detector, a path length of the first path being longer than a path length of the second path, the arrangement being such that, if a particle impinges on the splitter and a wavefunction of the particle is directed along both the first and second paths, the portions of the wavefunction that were directed along the first and second paths may interfere with one another at or near the detector.
  • the path length from the information particle source to the filter is less than the path length from the information particle source to the detection arrangement.
  • placing the filter in the on-path position is used to communicate a first binary state
  • placing the filter in the off-path position is used to communicate a second binary state
  • the method further comprises the steps of: providing a pair of path length modules, each of the path length modules having an input and an output and defining a path length therebetween, the path lengths of the path length modules being substantially identical to one another and hidden from an observer of the path length modules; and arranging the path length modules so that particles travelling from the information particle source to the filter pass through one of the modules and particles travelling from the information particle source to the detection arrangement pass through the other of the modules.
  • the method further comprises the step of providing a second filter and a second detection arrangement arranged so that the first filter is located near the second detection arrangement the second filter is located near the first detection arrangement.
  • the method further comprises the steps of: receiving, at the location of the first detection arrangement and the second filter, information from the location of the second detection arrangement and the first filter; and transmitting a confirmation signal to the location of the second detection arrangement and the first filter within a pre-set length of time after receiving the information.
  • the method further comprises the step of transmitting encrypted information.
  • Another aspect of the present invention provides a method for transmitting information comprising the steps of: providing a filter operable to act on a particle; providing an information particle source operable to emit particle pairs, the wavefunctions of the particles of the particle pair being entangled with one another, one particle in each pair being directed towards a detection arrangement and the other particle in each pair being directed towards the filter, the detection arrangement being operable to distinguish between one particle of a particle pair when the other particle of the particle pair has been acted on by the filter and one particle of a particle pair when the other particle of the particle pair has not been acted on by the filter; and moving the filter between an on-path position, in which the one particle in each particle pair passes though the filter, to transmit a first binary state to the detector, and an off-path position, in which the one particle in each particle pair does not pass though the filter, to transmit a second binary state to the detector.
  • FIG. 1 is a schematic view of a set-up wherein photons are incident on polarising beam-splitters
  • FIG. 2 is a schematic view of a first information transmission arrangement embodying the present invention
  • FIG. 3 is a schematic view of a second information transmission arrangement embodying the present invention.
  • FIG. 4 is an energy level diagram for an atomic system for use with the present invention.
  • FIG. 5 is a schematic view of an apparatus using the atomic system of FIG. 4 ;
  • FIG. 6 is a schematic view of a third information transmission arrangement embodying the present invention.
  • FIG. 7 is a schematic layout of a physically secure quantum channel
  • FIG. 8 is a schematic diagram of a source of spherically-distributed particles
  • FIG. 9 shows a schematic view of the components of a delayed-choice interference experiment
  • FIGS. 10 a to 10 c show diagrams assisting in the explanation of interaction-free measurement by repeated coherent interrogation.
  • FIG. 11 shows two space-time diagrams of nearly simultaneous events using two different approaches.
  • FIG. 1 shows the essence of the setup where an entangled source of photons, S is incident on polarizing beam-splitters (PBS) and then detectors picking up the horizontal and vertical photons.
  • PBS polarizing beam-splitters
  • ⁇ ⁇ s ⁇ ij 1 2 ⁇ ( ⁇ H ⁇ i ⁇ ⁇ V ⁇ j + ⁇ H ⁇ j ⁇ ⁇ V ⁇ i ) Eqn . ⁇ 2
  • ⁇ 1 is the angle of PBS 1 and ⁇ 2 is the angle of PBS 2
  • FIG. 2 shows a source (S) of entangled photons (pairs 1 and 2 ) as the communication channel. Distance between the polarising modulator and the interferometer is indicated by the double break in the lines showing the photon propagation.
  • S source
  • PBS polarising beam splitter
  • the probabilities calculated will only be very slight modulations in the output signal of the detectors for several reasons: most of the photons will not be entangled (only 1:10 10 from a typical down conversion process) and the optics and path lengths will be less than ideal. So the signal will ‘ride on top’ a large bias signal carrying no information but AC coupling from the detector to an amplifier can begin to discriminate this. Several tens of photons are sent per bit to allow for path differences between the two arms of the interferometer and accurate interference.
  • source 12 Since the horizontal component will not interfere with the vertical component from source (S) we regenerate the horizontal photon by entanglement with another source 9 12 via PBS 2 .
  • source 12 has the same power as source (S).
  • S On taking the tensor product of
  • an entangled photon is sent via the communication channel A. This achieved by making the distant polarising filter transparent. At the interferometer aspects of the incident photons (sources A and B) conspire to give minimal signal. Binary 1 occurs when the filter is either horizontal or vertical such that un-entanglement is transmitted.
  • a further method of sending classical data down a quantum channel as elaborated herein is to use Bell Inequalities relating to position and time as developed by Franson 14 .
  • This method can favour communication over fibre-optic cable for long distances 7 .
  • the essence is to generate entangled photons by a three level atomic system ( ⁇ 1 , ⁇ 2 , ⁇ Gnd ):
  • FIG. 4 Depicted in FIG. 4 is the energy level diagram for the atomic system.
  • ⁇ 1 When the system is energised from the ground state into state ⁇ 1 which has a lifetime of ⁇ 1 a photon ⁇ 1 is produced. The system then is in state ⁇ 2 which has a lifetime of ⁇ 2 which is considerably shorter than state ⁇ 1 .
  • R 12 ⁇ 1 ⁇ 2 0
  • the wavefunction at the detectors is (for particle one):
  • ⁇ ⁇ ( r 1 , t ) 1 2 ⁇ ⁇ 0 ⁇ ( r 1 , t ) + 1 2 ⁇ e i ⁇ 1 ⁇ ⁇ 0 ⁇ ( r 1 , t - ⁇ ⁇ ⁇ T )
  • R C 1 4 ⁇ R 12 ⁇ cos 2 ⁇ ( ⁇ 1 - ⁇ 2 )
  • the protocol once again is that a binary zero is represented by the act of no modulation (M) and binary one by collapse of the joint wavefunction between ⁇ 1 and ⁇ 2 .
  • the modulator is an absorber and can be an electronic shutter made from a Kerr or Pockels cell arrangement.
  • the bit time is longer than the transit time through the interferometer.
  • the lifetime of the second state, ⁇ 2 is longer than the transit time through the interferometer.
  • a full duplex quantum channel can be set up.
  • This channel is secure against “man in the middle attacks” because the information only exists at the extremities of the channel: any non-coherent measurement would collapse the wavefunction leaving only random noise; coherent measurement without the correct phase length would yield a constant binary digit as only entangled photons would be perceived. If the phase length could be guessed because the distance between the transmitting stations was well known, tapping into the channel would lead to massive obvious disruption and signal transmission loss; monitoring would catch this breach of security.
  • Nether-the-less further measures can be made by introducing a secret random phase length at both ends of the channel.
  • the length of fibre optic cable for instance, would be machine produced in matched pairs in a black box opaque to enquiry (by x-ray, ultrasound, terahertz radiation etc.) such that even the installer of the channel would not know the phase length.
  • a security seal system too would destroy the apparatus if it was not inserted into the correct machinery of the communication channel but say time domain reflection equipment to ascertain the secret phase length.
  • a secure docking procedure would do this.
  • a further aspect of the protection by the random phase length device would be if the eavesdropper was to guess a longer length as information exists after the modulation distance but not before.
  • a periodic acknowledge-protocol within the permitted time frame of the channel phase length and the random phase length would ascertain that the wrong length has been inserted.
  • Sub-nanosecond resolution would have the resolution to down to centimeters in a total channel length that could be kilometers. Phase lock would be a far from easy task.
  • FIG. 7 shows a schematic layout of a physically secure quantum channel as described above
  • 2 or ⁇ ( r,t ) d 3 r 1
  • FIG. 10 a shows an interferometer set up where a coherent photon source enters at the first beam splitter (partially silvered mirror) and recombines at a second.
  • the detector D-Dark has its coherence length set so that the beams interfere destructively whilst the detector D-Light is set for constructive interference.
  • FIG. 10 b an opaque object is placed in one arm of the interferometer. The firing of D-Dark indicates that a photon traversed the apparatus without interfering—that is it came down one arm only. Half of the time a photon will be absorbed by the object and the other half it will pass through to the detectors. We can say that the object has been detected with only half the incident number of photons into the measuring apparatus.
  • FIG. 10 c shows 8 the set up where by repeated coherent interrogations this 50% limit can be bettered and in the limit lead to no photons being absorbed by the object.
  • the wavefunction always measures the environment and can be made to traverse the apparatus many times not the photon, giving a vanishing probability of photon interaction with the object but growing certainty of its presence.
  • the lowest mirror switches out the interrogating wavefunction after a number of transits. A detector at a set interference length can work out if the side arm is blocked by the count of the detected photons.
  • the Lorentz Transform can be understood to have terms amounting to the transit time of light signals:
  • FIG. 11 shows two space-time diagram views of events very nearly simultaneous in time by a superluminal signal over a space-like interval with event A proceeding B.
  • the Lorentz view gets causality wrong, whilst the ‘expand and contract’ view of the axis gets it right.
  • the quotidian (3 space+1 time) view of objective reality is restored to space; events happen at a definite place and time agreeable by all observers—the Universe is a definite, objective stage in which the theatre of events occur.
  • phase A is a real function of co-ordinates that will be identified with the classical action and F is a real or complex function independent of time. Due to the smallness of h very rapid changes in phase result in this function over small distances; thus the wavefunction far away from the path of least action rapidly interferes and decays giving the notion of a classical path in the limit. Substitution of equation 4 in the Schrödinger Equation yields:
  • Quantum Reality 2 The Measurement Problem and Decoherence
  • Quantum Mechanics is a description of nature and equation 1 should always be true. However measurement throws the system into an eigenstate of the measurement operator and assigns a probability to it thus:
  • the diagonal components give the probability that the system is in either state, the off diagonal components the interference between the states.
  • the expectation of any observable represented by an operator A is given by the trace over the product of the density and operator matrices:
  • ⁇ n 1 ⁇ n 2 ⁇ n 3 8 abc ⁇ sin ⁇ ⁇ ⁇ ⁇ n 1 a ⁇ x ⁇ sin ⁇ ⁇ ⁇ ⁇ n 2 b ⁇ y ⁇ sin ⁇ ⁇ ⁇ ⁇ n 3 c ⁇ z
  • the dimensions of the box are a, b, c and taking the orthogonality condition for the two particles 1,2:
  • Quantum Mechanics saves reason and returns the Universe to an objective stage of 3-space and time where simultaneous events and material things too can be said to have occurred or existed at a definite place and time independent of measurement.
  • Classical ‘sentiments’ and intuition can return to physics in this way if we accept the primacy of a flow of the quantum state (and all that entails—the quantum rules) as a wave through 3-space and time (with relativistic effects of length contraction and time dilation) instead of a classical particle.
  • FIG. 2 shows a signal communication apparatus 1 .
  • the apparatus comprises an information particle sources, which is operable to emit particle pairs having indeterminate but related directions of polarisation.
  • the directions of polarisation of the particles are constrained to be different from one another by 90°. It will be appreciated that, for momentum to be conserved, the particles will be emitted in opposite directions.
  • the information particle source is configured so that a first particle in the particle pair is emitted in a first direction, towards a polarising filter 2 , and a second particle in the particle pair is emitted in a second direction, towards a detection arrangements, as will be described below in more detail.
  • the particles emitted by the information particle source are photons.
  • the polarising filter 2 is a filter that allows photons having a particular direction of polarisation to pass.
  • the polarising filter 2 is adapted to be placed in a first position, in which the first particle in each particle pair impinges on the filter, or in a second position, in which the first particle in each particle pair bypasses the polarising filter 2 and continues onwards.
  • the polarising filter 2 may be moveable between the first and second positions in a short period of time.
  • the modulation of the polarising filter 2 can be achieved by several means.
  • the path of the first particle can be switched between a transparent and polarized path with a switchable mirror.
  • electro-optic components such as Faraday rotators, Kerr and Pockel cells acting as electronic shutters can with the assistance of a polarizing beam splitter split the wavefunction of particle one into two channels, horizontal and vertical with dual synchronised shutters set at the appropriate angle for the horizontal or vertical channels.
  • a shutter on its own works by rotating the plane of the wave and to implement the transparent case to transmit binary zero we must have clear transmission—this could not be done with a single shutter because of its polarizing action when open.
  • the detection arrangement 3 comprises a polarising beam splitter 4 which is the first component of the detection arrangement that is encountered by an incoming particle.
  • the detection arrangement 3 also comprises a detector 5 , which is operable to detect particles of the type emitted by the information particle sources, and to provide an appropriate signal when a particle of this type impinges on the detector 5 .
  • First and second paths are defined between the polarising beam splitter 4 and the detector 5 , and a particle may travel along either of the paths to reach the detector 5 .
  • the polarising beam splitter is arranged so that incoming particles having a first direction of polarisation are directed along the first path, and incoming particles having a second direction of polarisation (which in the present example is preferably different from the first direction of polarisation by 90°) are directed along the second path.
  • suitably angled mirrors M are provided to guide particles travelling along the paths towards the detector.
  • first and second Faraday rotators 6 , 7 are located on each path so that a particle travelling along the first path has its direction of polarisation rotated by ⁇ /4 (i.e. 45°) and a particle travelling along the second path has its direction of polarisation rotated by ⁇ /4 (i.e. ⁇ 45°).
  • a single Faraday rotator may be located so that a particle travelling along the first path has its direction of polarisation rotated ⁇ /2 (i.e. through 90°).
  • a half-silvered mirror or another suitable device (not shown) is provided near the detectors to allow particles that have traveled along either of the paths to approach the detectors from the same direction.
  • the polarising filter 3 is placed slightly closer to the information particle source than the detector 5 is to the particle information sources. Therefore, by the time the second particle in each particle pair reaches the detector 5 , the first particle of the pair has either impinged on the polarising filter 2 , and so the direction of polarisation of the first particle in the pair (and, therefore, also the second particle in the pair) has been determined, or the first particle of the particle pair has bypassed the polarising filter 2 and the direction of polarisation of the first particle of the pair has not been determined, in which case the direction of polarisation of the second particle in the pair in also indeterminate.
  • the progress of a particle through the detection arrangement 3 either case will now be considered.
  • the particle will pass through the polarising beam splitter 4 and be directed along one of the arms of the detection arrangement 3 , depending upon the actual direction of polarisation. Whichever of the paths the particle is directed along, the particle will arrive at, and be detected by, the detector 5 and the arrival of the particle will cause the detector 5 to produce an appropriate signal.
  • the particle will be in a superposition of polarisation states.
  • a portion of the wavefunction of the particle corresponding to the particle having the first direction of polarisation will be directed along the first path, and a further portion of the wavefunction corresponding to the particle having the second direction of polarisation will be directed along the second path.
  • the directions of polarisation of the particles corresponding to these portions of the wavefunction are rotated by ⁇ /4 and ⁇ /4 respectively and will therefore be equal.
  • the two portions of the wavefunction will both arrive at the detector 5 and will combine with, and superimpose upon, one another.
  • the relative lengths of the two paths are set so that this superposition will result in destructive interference at the detector 5 , and so no particle will be detected.
  • the detection arrangement 3 is therefore operable to distinguish between an incoming particle whose direction of polarisation has been determined (by the polarising filter 2 being in the first position when the other particle of the pair reached the polarising filter) and an incoming particle whose direction of polarisation has not been determined (if the polarising filter 2 has been bypassed by the other particle of the particle pair).
  • a particle will be detected by the detector 5
  • no particle will be detected.
  • the polarising filter 2 When the polarising filter 2 is put into the vertical or horizontal position a measurement will be performed on the wavefunction for the first particle that will render collapse into solely the horizontal or vertical component—this signals binary one.
  • the modulation time should be sufficient for the second particle to traverse the interferometer apparatus and allow sufficient particles to trigger the detector and ensure a good signal to noise ratio.
  • the purpose of the Faraday rotators 6 , 7 is to manipulate the portions of the wavefuncton corresponding to particles travelling along the first and second paths so that they may interfere with one another.
  • a further example of a manipulation arrangement to fulfil this function will be described below.
  • FIG. 3 shows a second signal communication apparatus 8 embodying the present invention.
  • the apparatus comprises an information particle source, a polarising filter which is arranged at a distance from the information particle sources and a detection arrangement 9 which is also arranged at a distance from the information particle sources, so that particle pairs will impinge on the polarising filter 2 and detection arrangement 9 respectively.
  • the detection arrangement 9 of the second signal communication apparatus 8 is, however, different from that provided as part of the first, and this will be described in more detail below.
  • the detection arrangement 9 comprises a polarising beam splitter 4 which is arranged so that incoming particles having a first direction of polarisation are directed to the first path and incoming particles having a second direction of polarisation (different from the first direction of polarisation by 90°) are directed along the second path.
  • the second path simply comprises a suitably angled mirror M to deflect particles travelling along the second path towards the detector.
  • the first path includes a phase alteration component 10 through which particles travelling along the first path must pass, and the phase alteration component effectively adds a pre-set length to the effective path length of the first path.
  • the phase alteration component 10 may, for example be a block of glass having a very carefully machined length.
  • a further polarising beam splitter 11 is also provided on the first path.
  • the detection arrangement 9 is configured so that particles having a horizontal direction of polarisation are directed along the first path (with particles having a vertical direction of polarisation being directed along the second path) and the further polarising beam splitter 11 is arranged so that particles impinging thereon having a horizontal direction of polarisation are allowed to pass through the further polarising beam splitter 11 , and incident particles having a vertical direction of polarisation are reflected towards the detector 5 .
  • a further particle source 12 is also provided, arranged to emit particles (of the same type as those emitted by the information particle source) towards the further polarising beam splitter 11 .
  • the portion of the wavefunction of the particle from the information particle sources that travels along the first path is put into an additional superposition with the wavefunction of a particle emitted by the further particle source 12 , which will have a component corresponding to a vertical direction of polarisation.
  • This will allow interference at the detector 5 between the portions of the wavefunction of the incident particle that have traveled along the first and second paths.
  • the length of the two paths are chosen so that the two portions of the wavefunction will interfere destructively, resulting in no particle detection by the detector 5 . This is achieved by the introduction of the phase alteration component 10 which is located on the first path.
  • this detection arrangement 9 is also capable of distinguishing between an incoming particle whose direction of polarisation has been determined and an incoming particle whose direction of polarisation has not been determined.
  • two-way communication can be achieved by using two transmission arrangements in parallel with one another, but arranged for information to be transmitted in opposite directions.

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US11/793,104 2004-12-16 2005-12-16 Detection arrangement Expired - Fee Related US8184986B2 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB0427581.4 2004-12-16
GBGB0427581.4A GB0427581D0 (en) 2004-12-16 2004-12-16 Method for sending signals
PCT/GB2005/004860 WO2006064248A2 (en) 2004-12-16 2005-12-16 A detection arrangement for particles with two branches using superposition

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